The invention relates to a method for using the waste heat from a plant for producing cement, wherein heat of a process gas is used for heating water vapor via a heat exchanger, and wherein the plant for producing cement has at least one calcinator and at least one heat exchanger, which consists of a sequence of cyclones, for heating raw meal, and to a plant for producing cement, wherein the plant for producing cement has at least one calcinator and at least one heat exchanger, which consists of a sequence of cyclones, for heating raw meal.
Plants for producing cement generally handle large amounts of heat. In order to use the waste heat of a cement plant efficiently, the waste heat produced in the process is returned to the process via heat exchangers that are distributed in the plant. In the return of the heat, the recovery, it is necessary that the heat is returned to the process at as high a temperature as possible, in order to reduce the necessary input of energy for generating the process heat. However, not all waste heat that is produced in the plant is suitable for recovery. Generally, only those sources of heat that have a temperature well above 300° C. are recovered. Apart from returning the heat to the process, it is also known to use the unrecovered, low-calorific heat for drying raw material or to use it for preparing fuels.
Apart from the preparation of raw material and fuels, it has also become common practice to convert the unrecovered waste heat into electrical energy. In plants for producing cement, essentially two steam boiler systems are known for this. A first system is known as an SP boiler, from the concept of a “Suspension Preheater”, and this boiler is arranged downstream of the cyclone heat exchanger that is used in plants for producing cement for the preheating of the raw meal. A second system is known as an AQC boiler, from the concept of an “Air Quenched Clinker Cooler”, which is arranged downstream of a plant for producing cement in the exhaust air path of the clinker cooler.
However, on account of the low temperature of the unrecovered waste heat, these known systems for converting waste heat into electrical energy generally have an undesirably low conversion efficiency. This is so because, the higher the temperature of the waste heat, the greater the capacity of a general thermal engine to convert heat into mechanical work, which in turn is converted by a generator into electrical energy.
In order to improve the efficiency in the conversion of unrecovered waste heat into electrical energy in a plant for producing cement, it would consequently be necessary to create a source of waste heat that provides a much higher temperature than is known in known plants for producing cement.